The present invention relates to motor control centers and more particularly to a shutter mechanism for the motor control center.
Motor control centers, as well as other electrical equipment are equipped with draw-out type protective devices such as fusible disconnect switches or circuit breakers which are racked-in for establishing electrical contact with the bus bar assembly of the motor controller and are racked-out for breaking the electrical connection with the bus bar assembly. When the protective device is racked-out, it is desirable to close off access to the bus bar assembly to prevent inadvertent contact with the energized bus bars. Where there are several protective devices vertically arranged, the bus bars can remain energized when any one of the circuit breaker devices is removed. It is therefore desirable to close the opening to prevent inadvertent or unintentional contact with the energized bus bars.
Various shutter arrangements for preventing access to the bus bars when the protective device is racked out are illustrated in U.S. Pat. Nos. 4,183,073, 4,285,026 and 4,417,108. While the main function of a shutter mechanism is to close off the opening, it can be appreciated that it would be highly desirable to have a shutter assembly which is relatively simple and having few parts. The shutter assemblies illustrated in the above-mentioned patents have many parts and are quite elaborate devices. Generally, in a manufactured product, the higher the number of parts, the higher the manufacturing cost. Therefore, it will be appreciated that it would be highly desirable to provide a shutter mechanism which uses a small number of parts and is easy to manufacture and assemble.
A shutter mechanism which has a limited number of parts is illustrated in U.S. Pat. No. 4,146,915. While the number of parts has been reduced, there are still several parts, each of which must be manufactured and fitted together. Similarly, U.S. Pat. No. 4,486,815 illustrates a shutter device for the control unit of a control center which has relatively few parts. This shutter device does, however, have a tensioning spring which is a manufactured part which adds to the manufacturing cost. Accordingly, it would be appreciated that it would be highly desirable to provide a shutter mechanism for a motor control center which has few parts, is free of springs, is easy to assemble and economical to manufacture.
Accordingly, it is an object of the invention to provide a simple shutter assembly for a motor control assembly.
Another object of the invention is to provide a simple shutter assembly which operates without the use of springs.
Another object of the invention is to provide a shutter assembly which has few parts and is easy to manufacture.